Launch angle and backspin of golf ball have a great effect on trajectory of the golf ball hit by a golf club. The hit golf ball having large launch angle tends to have high trajectory, and the hit golf ball having small launch angle tends to have low trajectory. Since the backspin provides lift to the hit golf ball, the hit golf ball having large backspin amount tends to have high trajectory, and the hit golf ball having small backspin amount tends to have low trajectory. Performance requirements of golf balls from golfers include flight distance, shot feel, controllability and the like. When golfers use a golf club, particularly wood club (such as a driver), long iron club, middle iron club and the like, the flight distance is an important performance requirement.
In order to improve the flight distance when hit by a golf club such as a wood club, it is required for the hit golf ball to have high trajectory and long flight duration to a certain extent as well known. The hit golf ball having large launch angle and large backspin amount has high trajectory as described above, but the hit golf ball having too large backspin amount tends to have short flight distance. It is reason that kinetic energy is consumed by backspin, and that force applied such that the hit golf ball is pulled backward occurs by the lift until the golf ball reaches the highest point of the trajectory because the lift is applied perpendicular to the flight direction of the golf ball. Therefore, golf ball, of which the backspin amount is not very large and high trajectory is accomplished by high launch angle, has long flight distance when hit by a golf club, such as a wood club.
The shot feel is also an important performance requirement. When the shot feel is too hard, the golf ball has too short contact time with a golf club even if the backspin amount is small, and golfer can not easily hit the golf ball. On the other hand, when the shot feel is too soft, golfer feels that the golf ball has poor shot feel such that rebound characteristics are poor.
Based on the above knowledge, there has been many developments of golf ball having long flight distance accomplished by low backspin amount and high launch angle at the time of hitting, and good shot feel, from the viewpoint of formulation of the material and structure of the golf ball (Japanese Patent Kokai Publication Nos. 179798/1998, 267247/1999, 87422/2001 and the like).
In Japanese Patent Kokai Publication No. 179798/1998, a four-piece solid golf ball comprising a core, an intermediate layer composed of an inner intermediate layer and an outer intermediate layer, and a cover covering the intermediate layer is disclosed. The center has a diameter of 15 to 25 mm and a JIS-C hardness of 65 to 80, the inner intermediate layer has a thickness of 2 to 13 mm and a JIS-C hardness of 70 to 85, the outer intermediate layer has a thickness of 1.3 to 2.5 mm and a JIS-C hardness of 40 to 80, and the cover has a thickness of 1.7 to 2.9 mm and a Shore D hardness of 62 to 72.
In Japanese Patent Kokai Publication No. 267247/1999, thermoplastic composition for golf ball comprising (A) 40 to 95% by weight of polyamide-based thermoplastic elastomer, (B) 5 to 60% by weight of polyester-based thermoplastic elastomer and (C) 1 to 10% by weight of core-shell type polymer containing at least one of epoxy group and carboxyl group as an outer number of total 100% by weight of the (A) and (B) and having a Shore D hardness within the range of 20 to 50 is disclosed.
In Japanese Patent Kokai Publication No. 87422/2001, a multi-piece solid golf ball comprising a core composed of an inner layer core and at least one layer of an outer layer core formed on the inner layer, and at least one layer of a cover formed on the core is disclosed. The inner layer core has an elastic modulus of 50 to 200 MPa, the outer layer core comprises at least one layer of a low elastic modulus layer having an elastic modulus lower than that of the inner layer core by 15 to 100 MPa, at least one layer of the lowest elastic modulus layer having the lowest elastic modulus in the core has a total thickness of 0.2 to 5.0 mm and is placed in a range of 6.5 to 20.5 mm away from the center point of the core, and the core has a diameter of 37 to 41 mm.
However, it has been required to provide golf balls, of which the flight distance and shot feel are improved still more. Therefore, there has been no golf ball, which is sufficient to the balance between excellent flight performance by accomplishing small backspin amount and high launch angle at the time of hitting, and good shot feel at the time of hitting.